gpio: pca953x: Add NXP PCA9698

Add the NXP PCA9698 40-bit GPIO expander to the supported list.
Note: This only enables GPIO functionality.

Tested-by: Bob Schmitz <bschmitz@xes-inc.com>
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Acked-by: Graeme Smecher <gsmecher@threespeedlogic.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>